This invention relates generally to an electrical conductor and more particularly to the elongated inner conductor of a rigid coaxial transmission line of the type used in a broadcast antenna feeder system. Such a transmission line conventionally includes a relatively small diameter inner tubular conductor made of copper or the like and telescoped into a substantially larger diameter tubular outer conductor. The inner conductor is coaxial with the outer conductor and is held in spaced relation from the inner wall of the outer conductor by axially spaced insulating discs.
When high power is applied to and removed from the transmission line, the relatively small diameter inner conductor thermally expands and contracts in an axial direction to a greater degree than the outer conductor. To compensate for the differential thermal expansion and contraction, it is conventional to make the inner conductor in the form of multiple axially spaced sections and to couple adjacent ends of adjacent sections with a conductive connecting member which permits the inner sections to expand and contract relative to one another and the outer conductor while still maintaining an electrical joint between the inner sections. In one type of prior transmission line, the intermediate connecting member is a so-called bullet which is coupled to the inner conductor sections with a telescopic sliding fit to permit expansion and contraction. Repeated sliding of the components against one another, however, results in severe mechanical wear, produces metallic particles in the line and ultimately leads to line failure.
In another type of transmission line, an expandable and contractible bellows made of conductive material is connected between adjacent ends of adjacent inner conductor sections. While a bellows eliminates mechanical sliding contact, the previously used bellows is subject to severe sidewise distortion during assembly of the inner and outer conductors and then is subject to being overstressed in tension, compression and/or torsion during service use.